The invention relates to roadway structures in the form of continuous multi-layer composite slabs that are supported by an elastic foundation.
One known arrangement of this type is described in U.S. Pat. No. 2,083,900. In such arrangement, a three-layer slab is described wherein the superposed layers are all approximately equal in thickness (e.g., 1-2 inches). Additionally, the porosity of the composite layer of the structure described in such patent decreases progressively from the lower to the upper layers of the structure.
One disadvantage of such known structure is that, because of the relatively high porosity of the lowermost layer of the slab, water and mud in the underlying foundation are permitted to seep upwardly through the several layers of the slab, thereby exerting a weakening effect thereon. In addition, with the successively increasing porosity of the slab toward the bottom thereof, extremely low atmospheric temperatures can rather easily propagate from the surface of the slab down to the foundation, thereby setting up a destructive freezing-thawing phenomenon.